Along with the widespread use of a digital camera, a camera-equipped cell phone and the like, the market of the solid-state imaging apparatus has been remarkably developed. In this flow of development, it is expected that the development of a high resolution and high sensitivity of the solid-state imaging apparatus is accelerated.
In the present, in a charged-coupled device (CCD) and a metal oxide semiconductor (MOS) imaging sensor that are commonly used as solid-state imaging apparatuses, semiconductor integrated circuits having multiple light-receiving portions are arranged in a two-dimensional array, in which a light signal from an object is converted into an electric signal.
The sensitivity of the solid-state imaging apparatus is defined based on an amount of output current of a light-receiving device to the amount of incident light so that leading the incident light certainly into the light-receiving device is an important factor for the improvement of sensitivity.
FIG. 1 shows an example of a conventional structure of a general pixel. A solid-state imaging apparatus (unit pixel for blue light) 70 includes a microlens 33 which collects incident light, a color filter 2 which separates and transmits blue (B) light from the incident light, a light-receiving device (Si photodiode) 6 which converts the incident light into charge, an electric signal transmitting unit 4 for transmitting the charge, Al wirings 3, planarized layers 5 and a Si substrate 7. The solid-state imaging apparatuses for read light (R) and green light (G) have the same structure except the fact that the color filter 2 only differs. Relatively high light-collection efficiency can be obtained by such structure. Therefore, the microlens 33 is used in almost all solid-state imaging apparatuses. Whereas various technologies are disclosed as a solid-state imaging apparatus using a Fresnel lens (e.g. refer to First Patent Reference and Second Patent Reference).
In the technology disclosed in the First Patent Reference, the lens is made up of multiple layers that are concentrically formed, each of which has a unique refractive index. The center part of the concentric circle structure has the highest refractive index as the refractive index decreases toward the direction of the peripheral part. Also, in the technology disclosed in the Second Patent Reference, a thickness distribution type lens and a distribution refractive index type lens which has a consecutive refractive index distribution by doping are used.
Patent Reference 1: Japanese Laid-Open Patent Publication No. 2000-39503
Patent Reference 2: Japanese Laid-Open Patent Publication No. 5-251673